For nearly forty years, since the advent of the heart-lung machine, it has been possible to reconstruct and replace heart valves.
The concept of repairing, rather than replacing, diseased heart valves began with the work of Professor Ake Senning of Zurich in 1960. (Senning A:Fascia lata replacement of aortic valves. Journal of Thoracic Cardiovascular Surgery 54:465-470 (1967)). Senning used autologous fascia lata to fashion three-dimensional aortic valve repairs with a freehand technique, but subsequently abandoned his method by 1970 because of valve failures from thickening and shrinkage of the fresh, untreated tissue. Because of the experiences of Senning and others using similar techniques to repair or reconstruct heart valves with fresh autologous tissue, focus in the field of heart valve disease shifted from valve repair and reconstruction to full valve replacement with mechanical prostheses, and later, with bioprostheses made from heterograft (animal) tissue supported by a plastic or metal stent or frame.
Mechanical valves, such as the St. Jude Mechanical Bileaflet Valve, are often preferred because they have indefinite durability. Mechanical valves, however, also have inherent disadvantages, such as, for example, the danger of inducing blood clotting, thus requiring most patients to be on life-long anticoagulation medication. Mechanical valves also have less than ideal hemodynamic (blood flow) properties, they can be noisy, and the structural failures associated with such valves are usually catastrophic. Additional disadvantages are well known to those skilled in the art.
Heterograft (animal) tissue valves typically employ a semi-rigid frame, or stent, which supports animal tissue leaflets. Such stents are attached to the patient's heart with sutures. Tissue valves were originally believed to provide answers to most of the problems associated with mechanical valves: they significantly reduce the need for anticoagulation therapy, they have better, though not ideal, hemodynamic qualities, they are quiet, and their failure modes are generally slower, allowing time for surgical intervention to replace a failing valve. Clinical experience, however, has shown that such tissue valves have limited durability, for example, on the order of five to fifteen years. This limited durability is usually due to calcium build up on the foreign tissue, known as calcific degeneration, and is thought by several investigators to be caused by an immune response to the presence of a foreign tissue. There are also inherent disadvantages to using such frames, or stents, such as, for example, the space the stent occupies in the annular area thereby reducing effective valve orifice area, and possible abrasion of the tissue against the stent thereby causing or contributing to primary tissue failure of the valve.
Beginning in 1985, Love suggested using autologous pericardium, treated with a brief immersion in a glutaraldehyde solution, for use in an autologous tissue replacement for heart valves (Love et al. "Rapid intraoperative fabrication of an autogenous tissue heart valve: A new technique." Proceedings of the Third International Symposium on Cardiac Bioprostheses 691-698 (1986)). Later, Love reported that autologous pericardium, briefly treated in glutaraldehyde, does not thicken or shrink, is resistant to calcific degeneration, and is durable beyond 25 equivalent years in the accelerated life tester. (Love et al. Experimental evaluation of an autologous tissue heart valve. Journal of Heart Valve Disease, 1992; 1232-241). Others, such as Carpentier, a physician working on problems with the mitral valve, showed similar results (Chauvaud et al. "Valve extension with glutaraldehyde-preserved autologous pericardium" Journal of Thoracic and Cardiovascular Surgery 102:171-178 (1991)). Duran, another physician, resurrected Senning's techniques, and has used autologous pericardium treated with a brief immersion in glutaraldehyde for repair of diseased aortic valves, with good results, including lack of calcification. (Duran et al. "Indications and limitations of aortic valve reconstruction" Annals of Thoracic Surgery 52:447-454 (1991)).
In spite of the discovery that glutaraldehyde-treated autologous tissue, as opposed to fresh, untreated tissue, can be used as a material for heart valve replacement or repair, significant problems still exist with all of the reported approaches for repairing and reconstructing heart valves including, but not limited to, semilunar heart valves. These problems include, for example, that they are not standardized and they do not employ a relatively precise, pre-designed, reproducible, optimized pattern of two-dimensional tissue which, when attached to the aortic annulus and pressure loaded at physiologic levels, achieves normal or near normal three-dimensional anatomy when used to function as a semilunar heart valve.
In order to overcome the disadvantages of the prior art, as those skilled in the art will recognize and appreciate, there is an established need for an improved, more easily reproducible, less complicated, generally standardized, design and method of making a unitary valve tissue pattern to be used for the repair or reconstruction of a semilunar heart valve, having a generally simulated anatomical shape and good blood flow characteristics. The claimed invention provides a new, useful and unique two-dimensional valve tissue pattern design and method which may be used for easily fabricating three-dimensional heart valves for heart valve repair or reconstruction, which overcome many of the disadvantages of the prior art.